1. Field of the Invention
The present invention relates to a flexible disc cassette such as floppy disc or the like used for magnetic disc cassette recording and/or reproducing apparatus.
2. Description of the Prior Art
A conventional disc cassette of this type comprises a disc-shaped flexible magnetic sheet which is held between upper and lower halves. A head access hole is formed in one of the upper and lower halves. Further, a shutter which is capable of opening/closing the head access hole is mounted on the cassette case such that the intrusion of dust and the foreign substances into the cassette can be prevented. The shutter is normally biased by a coil spring or the like in the position where the head access hole is closed.
In such a conventional structure, when the cassette is loaded into or removed from the recording and/or reproducing apparatus, the shutter can be automatically moved to the open or closed position, so that it is very convenient for a user. However, since a small spring must be mounted in the cassette, the man-hour of assembly is increased, so that it becomes inconvenient for a manufacturer. Particularly, when automatic disc cassette assembling machine is used, it is more difficult to handle elastic members such as a coil spring than rigid members. Therefore, special implementation and proper adjustment are required in the holding means and insertion means (mount means) of the automatic assembling machine.
The present inventor, therefore, has previously proposed a flexible disc cassette in which a torsion spring is used for urging a shutter, as shown in FIG. 1. Referring to FIG. 1, a torsion spring 1 is made by winding, for example, a stainless steel wire several turns to constitute a coiled portion 2. Both tips 3 and 4 of the coiled portion 2 linearly extend along the tangential direction of the coiled portion 2. One U-shaped tip 3 engages with the pin formed inside one of the upper and lower halves. The other tip 4 is bent substantially perpendicularly and is locked with the stop of the shutter. When the U-shaped tip 3 is closely fitted around the pin of the half, the spring 1 is mounted inside the half. Further, since the other tip 4 can be stopped at the stop of the shutter by the biasing force of the spring 1 itself, automatic or manual assembly can be easily performed.
However, since the tip 3 of the spring 1 has a complex shape, it is difficult to manufacture the spring 1. In addition, since the dimensional accuracy of the tip 3 is not high, the tip 3 is often released from the pin of the half because of its weak elastic fitting force, and cannot be automatically assembled because of variations in optimal fitting angles. Furthermore, the springs become entangled with each other to degrade the assembly efficiency.